[HOW TO SEND A FILE SECURELY BY EMAIL]

Encrypt the file, send it, and get the password to the recipient by a different route.

An ordinary email attachment is protected while it travels between mail servers (usually by TLS), but it is stored readable in the sender's and recipient's mailboxes, on the providers' servers and in every backup of them. Anyone who gets into either account — or who receives a forwarded copy — can open it. For a contract, a scan of an ID card or medical records, that is not good enough.

The fix is simple: encrypt the file before attaching it, and send the password separately.

[METHOD 1: ENCRYPT THE FILE, THEN ATTACH IT]

  1. Encrypt the file with a password: in your browser with the file encryption tool, or with 7-Zip using the 7z format and AES-256 (tick "Encrypt file names").
  2. Attach the encrypted file (.enc or .7z) to a normal email. It is safe for it to sit in mailboxes and backups: without the password it is noise.
  3. Send the password by another channel — see below.
  4. The recipient opens the file with the same tool: decrypt it in the browser, or with 7-Zip for a .7z.

This works with any email provider and any recipient, and the protection travels with the file wherever it is forwarded or stored.

[METHOD 2: AN END-TO-END ENCRYPTED EMAIL SERVICE]

Proton Mail and Tuta encrypt messages and attachments end to end between their own users, and can send password-protected messages to people on other providers. This is the most convenient option if you exchange sensitive files regularly.

Note that Gmail's "confidential mode" is not encryption: it adds an expiry date and blocks forwarding in the interface, but Google can still read the content and the recipient can take screenshots.

[METHOD 3: AN ENCRYPTED SHARING LINK FOR LARGE FILES]

Gmail and Outlook cap attachments at around 20–25 MB. For larger files, encrypt the file first, upload the encrypted copy to any cloud service, and email the sharing link. The cloud provider only ever stores ciphertext. (Proton Drive and Tresorit offer end-to-end encrypted links directly.)

[HOW TO SHARE THE PASSWORD]

  • Never in the same email, and not in a reply to it. Anyone who reads the email would then have both halves.
  • Use a different channel: a phone call, a text message, or an end-to-end encrypted messenger such as Signal or WhatsApp.
  • Agree on it in advance if you exchange files often, so nothing needs to be sent at all.
  • Use a long password — four or five random words, or 16+ random characters. Encryption is only as strong as the password.

[MISTAKES TO AVOID]

  • Password-protected ZIPs made with Windows' built-in tool use the legacy ZipCrypto scheme, which can be broken. Use AES-256 (7-Zip) instead.
  • PDF "permissions" passwords that only block printing or copying protect nothing: any PDF tool removes them. Only a password needed to open the document encrypts it.
  • Readable file names. "2024_salary_review_John_Smith.pdf.enc" already leaks information. Rename the file before encrypting it, or put it in an archive with encrypted file names.
  • Leftover copies. Delete the unencrypted original from your Downloads folder and the "Sent" copy of any earlier unencrypted attempt.

[HOW TO SEND AN ENCRYPTED FILE BY EMAIL]

Encrypt a file before attaching it to an email, and share the password safely.

  1. Encrypt the file. Encrypt it with a strong password, in the browser or with 7-Zip (AES-256).
  2. Attach and send. Attach the encrypted file to a normal email.
  3. Send the password separately. Give the password by phone, text message or an encrypted messenger — never in the same email.
  4. Recipient decrypts. The recipient opens the file with the same tool and the password.

[FREQUENTLY ASKED QUESTIONS]

Is email encrypted by default?

Only in transit between servers, usually with TLS. Messages and attachments are stored readable in both mailboxes and on the providers' servers. End-to-end encryption needs a service such as Proton Mail, or encrypting the file yourself.

Does the recipient need to install anything?

No. A file encrypted on CryptFile.Online can be decrypted on the same website in any modern browser, on a computer or a phone.

What if the file is too large to attach?

Encrypt it, upload the encrypted copy to a cloud service such as Google Drive or Dropbox, and email the sharing link. The provider only stores encrypted data.